Certain power-steering drives having a single-stage or two-stage belt transmission are conventional. In two-stage belt transmissions, the belt pulleys may have a smaller diameter as compared to a power-steering drive having a single-stage belt transmission, because the overall transmission ratio results from a product of the individual transmission ratios. A disadvantage in conventional power-steering drives is the limited, maximally possible transmission ratio since the available space is limited. In very large transmission ratios, the driven belt pulley must be selected to be so large that there is hardly a chance for installing it in a motor vehicle. A large transmission ratio is desirable, however, if one wants to achieve high servo torques using relatively small electric motors.
It is furthermore conventional to use power-steering drives having worm transmissions. In this instance, the worm is coupled by a dog clutch to the motor shaft for example. The worm normally drives a worm wheel connected in a rotatably fixed manner to the steering shaft. Often, the worm is adjusted to the worm wheel to prevent bothersome noises. The worm transmission is likewise limited in terms of transmission ratio since otherwise the efficiencies for turning in and/or turning back become too unfavorable.